Device of the kind comprising an energy amplifying tube having a pentode characteristic curve



y 7, 1956 2. VAN GELDER 2,755,411

DEVICE OF THE. KIND COMPRISING AN ENERGY AMPLIFYING TUBE HAVING APENTODE CHARACTERISTIC CURVE Filed Dec. 17, 1952 I I I I K 2 I S I j i-q 50- III 1 VOLTS ANODE Fig.l

INVENTOR ZEGER VAN GELDER AGENT United States Patent DEVICE OF THE KINDCOMPRISING AN ENERGY AMPLIFYING TUBE HAVING -A PENTODE CHARACTERISTICCURVE Zeger Van Gelder, Eindhoven, Netherlands, assignor to HartfordNational Bank and Trust Company, Hartford,

Conn., as trustee Application December 17, 1952, Serial No. 326,445Claims priority, application Netherlands February 2, 1952 5 Claims. (Cl.315-13) contrary, is high and drops comparatively strongly at anincrease in Va and assumes a definite, comparatively low, substantiallyconstant value at the knee. voltage. Since such tubes usually operate atanode voltages exceeding the knee voltage, the screen grid of such tubesis proportioned to be such that at this comparatively low screen-gridcurrent noexcessive heating of the screen grid occurs. However, inenergy amplifying tubes the heating brought about by the screen-gridcurrent is yet so great that, as a rule, particular measures .must betaken to cool the screen grid. For this purpose the screengrid wireshave been arranged behind thecontrol-grid wires and cooling members havebeen provided at the screen-grid stay wires. However, these means areinsufficient in those cases. in which the anode voltage is often lowerthan the knee voltage, so that excessive heating of the screen-grid mayoccur. This is the case, for example, in definite transmitting tubes andtelevision tubes.

In this case the provision of larger cooling members does not remedy theevil, since the comparatively thin screen-grid wires themselves cannottransmit the heat sufliciently rapidly to the stay rods or the coolingmembers. These wires must be thin, in' order to intercept a minimum ofprimary electrons.

' Extensive experiments have nowshown that the said difliculty can besubstantially completely avoided, if, in accordance with the invention,in a device comprising an energy amplifying tube having a pentodecharacteristic curve, in which the electrons emanating from the cathodeare concentrated in one or more beams, a number of screens with positivepotential are arranged outside the forward electron flow in closeproximity to the screen grid. It has been found that these screens arecapable of attracting and intercepting the primary electrons which arereflected owing to the spatial charge between the screen grid and theanode.

The electrons reflected by a spatial charge occurring in front of theanode produce a strong increase in screengrid current at low anodevoltages. By using a tube according to the invention excessive heatingof the screengrid wires can be avoided even at low anode voltages. Itwas a surprise to find that the reflected electrons, which are otherwiseintercepted by the positive screen-grid wires are sufliciently attractedby the positive screens according to the invention to find their way tothese screens.

The difficulty caused by reflected electrons also occurs in mixing tubesand electronically coupled mixing tubes 2,755,411 Patented July 17, 1956and oscillator tubes, inter alia in hexodes, octodes and the like.However, with energy amplifying tubes the conditions are quite differentfrom those occurring in such mixing tubes in which the electronsreflected electrostatically by a control-electrode are reflected in adefinite direction. In such tubes the construction of the grids istherefore such that the reflected electrons are directed to screensprovided for this purpose. Since such tubes operate with a low electroncurrent, it may be ensured that the electrostatically determinedelectron paths are affected very little by spatial charge. This is,however, quite different in energy amplifying tubes in which thereflection of electrons occurs more or less irregularly, if high spatialcharges occur locally at definite instants. I

In order that the invention may be readily carried into effect, it willnow be described in detail with reference to the accompanying drawing,in which Fig. 1 shows a graph of apentode;

Figs. 2 and 3 show tube constructions according to the invention;

Fig. 4 shows the tube illustrated in Fig. 3 in a typical operatingcircuit.

.Referring now to Fig. 1, reference numeral I designates the IaVacharacteristic curve of a tube having pentode characteristics, and IIdesignates the I a-Va characteristic curve of the screen grid of such atube. At an anode voltage of less than 25 to 50 v., the screen-gridcurrent increases very strongly, so that the known tubes are practicallyunserviceable at such anode voltages, since the screen-grid is thenoverloaded. This may be avoided, if for example use is made of an energyamplifying tube of a construction according to the invention, as isshown in Figs. 2. and 3. Fig. 2 shows a spatial-charge tetrode, in which1 designates the cathode, 2 the control-grid, 3 the screen grid, 4 theanodes and 10 the bulb of the tube. The screens 5, which may, ifdesired, be replaced by a collecting grid, may be connected tothecathode 1, or be connected outside the tube to zero' potential or tolow potential. They may produce at7 a spatial charge, if the anodevoltage has a low value, so that the secondary electrons 8 from theanode are withheld and the pentode .characteristic curve shown in Fig. lis produced. It is found that the electrons 9, reflected by the spatialcharge, may be attracted by the screens 6, which are kept on acomparatively high positive potential and which may, if necessary, beconnected in'the tube to the screen grid 3 in a manner such that theseelectrons find their way to these screens instead of to the positivescreen-grid wires. evident from curve III of Fig. 1, which indicates thevariation of the current of these screens 6. Moreover, it is thusavoided that the reflected electrons should pass several times throughthe system and might produceBarkhausen- Kurz oscillations. The currentof the screen grid itself appears to have a variation in accordance withcurve 'IV of. Fig. 1. It is evident that at a low Va this exceeds onlylittle that at a high Va. Thus also in the range of low Va excessiveheating of the screen-grid wires may be avoided.

It is necessary that the flow of electrons should be concentrated inbeams, since otherwise the reflected electrons should traverse in anydirection the forward flow of electrons, so that no measures could betaken to intercept only these reflected electrons, since the arrangementof positive screens outside the forward flow of electrons would then notbe possible and these screens would then intercept also a great portionof the forward going electrons.

In general, the provision of a control-grid with stay rods suffices toform the beams. This is, for example, the case with a tube as shown inFig. 3, in which the invention has been carried out in a pentodeenergy-amplifying tube, comprising a collecting grid. In this figurereference numeral 11 designates the cathode, 12 the control-grid, 13 thescreen-grid, 14 the suppressor grid or collecting grid, 15 the w in Thisis anode and 17 the bulb of the tube. In the proximity of the stayrcdsofthe screen grid 13 are provided the screens 16 according to theinvention. In certain cases these screens themselves may beshaped asstay members, over which'the screen-grid wires are wound. However, as amile, it is preferred to arran e and to shape these screens so that theyare located not only outside the forwardgoing bearn's, but also for themajor part outside the plane of the screen-grid Wires, so that thesucking effect on the electrons, wandering back comparatively slowly, isimproved and a minimum quantity of these electrons will find their wayto the screen-grid wires themselves. This is particularly of importance,if comparatively wide beams are used, as is the case shown in Fig. 3.The screens may be connected internally to the screen grid. typicalciredit for the tube of Fig. 3 is illustrated in Fig. 4, which shewsthesuppressor grid 14 connected to the cathode 11, and the screens 16connected internally to the screen grid 13, both therefore being at arelatively high potential relative to the cathode 11.

The eifect of the invention is consequently obtainable only if the flowof electrons is divided into limited beams and it the current density inthe beams is so high thatelectrons can be reflected by a high spatialcharge. Consequently, the invention is of importance, in general, onlyfor power amplifying tubes, i. e. tubes adapted to operate with acomparatively high electron current, for example, with a mean anodecurrent of more than 25 ma. A The invention is furthermore of importancefor all those cases in which electrons reflected by spatial charges giverise to excessive heating of preceding positive grids of thin wires.

Apart from the embodiment shown, other embodiments of the invention arepossible. For example, the screens according to the invention may beprovided with a sep- 'arate current supply conductor and be quite freefrom screen grid, but they may, as an alternative, be connected directlyto the screen grid. In this case a tube according to the inventioncomprises two sets of plate-shaped electrodes arranged between thescreen grid and the anode, these electrodes being arranged clearlyoutside the path of the forward flow of electrons, the set nearest thescreen grid being connected to this screen grid, the other set to thecathode.

What I claim is:

1. A beam power discharge device having a pentode anode voltage-anodecurrent characteristic for operation with high anode currents,comprising a cathode, control grid, screen grid, suppressor electrodeand anode disposed in that order within an envelope, said electrodesbeing arranged to confine the electron flow between the cathode andanode in a limited area, means for applying a comparatively highpositive potential relative to the cathode to thescreen grid and notmore than a low positive potential relative to the cathode to thesuppressor electrode to thereby produce a high space charge region inthe path of the electron fi'ow between the anode and screen grid 4.whereby the tube exhibits a pentode characteristic, a plurality ofscreens disposed in close proximity to and outside of the screen gridand outside the path of the electron flow, and means connecting saidscreens to said screen grid to attract primary electrons reflected bythe space charge region and thus prevent them from striking the screengrid.

2. A beam power discharge device as claimed in claim 1 in which thescreens comprise a pair of bent oppositelydisposed plate-shapedelectrodes disposed between the screen grid and the suppressorelectrode, each of said electrodes partially embracing a portion of saidscreen grid.

3. A beam power discharge device as claimed in claim 1 in which thesuppressor electrode comprises a first pair of oppositely-disposed bentplate-shaped electrodes located outside the path of electron flow, thescreens comprise a second pair of oppositely-disposed bent plate-shapedelectrodes disposed coaxially within said first pair and outside thepath of electron flow and partially embracing the screen grid, and meansare provided connecting the suppressor electrode to the cathode.

4. A circuit including a beam power discharge tube having a pentodeanode voltage-anode current characteristic for operation with high anodecurrents, said tube comprising a cathode, control grid, screen grid,suppressor electrode and anode disposed in that order within anenvelope, said electrodes being arranged to confine the electron fiowbetween the cathode and anode to a limited area, a plurality of screensdisposed in close proximity to and outside of said screen grid andoutside the path of the electron flow between the cathode and anode,means for maintaining, the screen grid at a comparatively high positivepotential relative to the cathode, means for maintaining a potentialbetween zero and a low positive potential relative to the cathode on thesuppressor electrode to thereby produce a high space charge region inthe path of the electron flow between the anode and screen grid wherebythe tube exhibits a pentode characteristic, and means for maintainingsaid screens at a comparatively high positive potential relative to thecathode and of the order of that maintained on the screen grid toattract primary electrons reflected by the space charge region and thusprevent them from striking the screen grid.

5. A circuit as claimed in claim 4 wherein the screens comprise a pairof bent oppositely-disposed plate-shaped electrodes disposed between thescreen grid and the suppressor electrode, each of said electrodespartially embracing a portion of said screen grid.

References Cited in the file of this patent UNITED STATES PATENTS2,113,801 Shoenberg et a1 Apr. 12, 1938 2,219,102 Herold Oct. 22, 19402,228,978' Schade Jan. 14, 1941 2,460,382 Fulton Feb. 1, 1949

